A conventionally proposed linear motor comprises a magnet member composed of round-shaft-like permanent magnets having alternately arranged respective N poles and S poles, and a coil member having a plurality of coils arranged in an axial direction so as to surround the periphery of the magnet member (for example, the Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 10-313566).
The linear motor disclosed in the Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 10-313566 is used, for example, in OA equipment or the like in place of a combination of a rotary motor and a ball screw. However, using the linear motor in a machine tool such as a press machine which makes direct-acting motion also results in a simple configuration and enhanced controllability.
Where the linear motor is used in a press machine or the like, when, for example, a movable portion such as a ram is stopped at an elevation standby position, the movable portion can desirably be stopped without falling down even though a motor power supply is turned off for power saving or the like. Further, even if the power supply is not turned off at the elevation standby position, for safety, the movable portion such as the ram is preferably prevented from falling down inadvertently and maintains the stopped position when a power supply system becomes defective. To prevent the possible fall-down, it is possible to use a spring or an air cylinder. However, this disadvantageously increases the number of parts required, complicating the structure.
An object of the present invention is to provide a linear motor that can use a simple configuration to prevent the magnet member from moving inadvertently when the power supply is turned off. Another object of the present invention is to provide a linear motor that can use a simple configuration to prevent the magnet member from falling down when the power supply is turned off. Yet another object of the present invention is to provide a linear motor control device which can prevent the magnet member from falling down when the power supply is turned off and during operation, inhibit fall-down preventing means from imposing excess loads during operation. Still another object of the present invention is to provide a linear motor mounted machine tool which has a simple structure owing to the need for a reduced number of parts required and which can be prevented from operating inadvertently when the power supply is turned off, improving safety.